JP2002-021573A published by the Japanese Patent Office in 2002 discloses a turbocharger and an electric supercharger used together for an internal combustion engine for vehicles, in order to obtain a desirable supercharging performance.
The electric supercharger comprised a compressor driven by an electric motor, this compressor and the compressor of the turbocharger being arranged in series in an engine intake passage.
JP2000-230427A published by the Japanese Patent Office in 2000 discloses an electric supercharger in the intake passage of an internal combustion engine, and a bypass valve which bypasses the electric supercharger. The bypass valve is closed when the electric supercharger is operated, i.e., during supercharging, and is opened when the electric supercharger is not operated, i.e., during natural aspiration.